The interface reactions of FeO/Cr, Cu2O/Ni (undoped and doped), TiAl/Al2O3, Ti/Al2O3, and TiAl/TiO2 and the oxidation of TiAl have been investigated, and the reaction paths of these reactions have been analyzed in chemical potential diagrams. The reaction paths of the interface reactions are dependent on the thickness of the sample and on the reaction time. The reaction paths and the diffusion behavior of these interface reactions have been reasonably explained by a simple model assuming a local equilibrium at the interfaces which predicts that the reaction path should be represented by lines in the chemical potential diagrams. Examples of computer simulations using chemical potential diagrams are presented as a tool in the design and control of the metal/oxide interface reactions.